This invention relates generally to valves and, more specifically, a check-relief valve for use in hydraulic fluid circuits.
Check-relief valves are well known in the art. Such valves essentially combine the functions of both check and relief valves into one body. Check valves control the direction of flow of fluid, allowing fluid flow to travel only in the direction of lower pressure. Check valves prevent backpressure from reversing the flow of a fluid circuit. Relief valves serve as a vent for excessive backpressure. When backpressure exceeds a threshold level, a relief valve will open to prevent backpressure from increasing and damaging the fluid circuit. The advantage of check-relief valves is the conservation of space gained by bringing two functions into a single body.
Conventional cartridge-style check-relief valves comprise a guide with a centrally-located stem. The stem is connected to the dampening disk at one end of the stem and is critical to the relief function of the valve. The guide and stem combination ride within a base or plug. The guide has a seat on the side opposite the plug. The valve normally remains in a closed position, which is where no fluid flows past the valve. In operating as a check valve, pressure drives the guide and stem combination of the conventional device into the plug, forcing the seat to move to an open position and allow fluid flow. When fluid flows past seat, the valve is said to be in the check position. The greater the clearance between the outer diameter of the dampening disk and the inner diameter of the plug, the greater the rate of fluid flow past the dampening disk and the faster the valve will be able to move into the check position. A check spring, which is of the helical compression type, works to resist the movement of the guide and stem combination and will reseat the valve upon a certain diminished level of pressure.
In operating as a relief valve, backpressure of a threshold level will drive the dampening disk and stem combination of the conventional device away from the plug. Because the seat already is in the closed position, a gap opens between the stem and seat, allowing the backpressure to vent. When fluid flows through the gap between the stem and the seat, the valve is said to be in the relief position. A relief spring, which also is of the helical compression type, works to resist the motion of the dampening disk and stem combination and will return the stem to a closed position upon a certain diminished level of backpressure. The smaller the clearance between the outer diameter of the dampening disk and the inner diameter of the plug, the greater the dampening capacity of the disk and the greater the stability of the system will be.
With conventional cartridge-style check-relief valves, it is desired to have a large clearance between the plug and the dampening disk in order to optimize the performance of the check function and minimize the time needed to move the valve into the check position. In a hydrostatic pump situation, a flash check time is partially desired when beginning operation from a cold start. Yet, it also is desirable to have a small clearance between the plug and dampening disk in order to maximize the dampening capacity of the valve when moving into the relief position. This leads to greater stability through the fluid circuit. In a hydrostatic pump situation, greater dampening capacity is desired when operating at higher temperatures.
A disadvantage of conventional cartridge-style check-relief valves is that the clearance parameter is restricted only to one value. As such, both the check and relief functions of the valve are governed by the same clearance parameter. Essentially, this means that one of the functions, check or relief, must be compromised as it is only possible to optimize one function at a time. Either there will be a large clearance between the outer diameter of the dampening disk and the inner diameter of the plug, which benefits the check function, or the clearance will be small, which benefits the relief function.
It is therefore a principal object of this invention to provide a check-relief valve that allows for a quick check response time while still allowing for sufficient relief dampening and fluid circuit stability.
Another object of this invention is to provide a check-relief valve that allows for separate clearance parameters for both the check as well as the relief functions of the valve.
A further object of this invention is to provide a check-relief valve with separate check and relief clearance parameters that minimizes the number of components.
Another object of this invention is to provide a check-relief valve with separate check and relief clearance parameters than conserves physical space.
Yet another object of this invention is to create a check-relief valve with separate check and relief clearance parameters that minimizes manufacturing time and cost.
These and other objects will be apparent to those skilled in the art.